Bertha is tunneling Seattle’s underground freeway

Bertha the 57.5 feet in diameter tunneling machine has arrived in Seattle, to replace the SR 99 Alaskan Way Viaduct while minimizing closures of the highway during construction.

This short video provides an overview of Bertha’s journey and the work WSDOT is doing to replace the freeway.

Tunneling beneath Seattle allows usWhen the tunnel opens in late 2015, a two-mile stretch of SR 99 will move underground, allowing us to remove the viaduct and clear the way for new public space along Seattle’s downtown waterfront.

“At 57.5 feet in diameter – roughly as tall as a five-story building – our tunneling machine is the world’s largest. The machine was shipped to Seattle on the Jumbo Fairpartner, after successfully undergoing testing in Osaka, Japan, where it was built. It arrived in Elliott Bay on April 2, and it will be reassembled in an 80-foot-deep pit to the west of Seattle’s stadiums in the months ahead. Tunneling is scheduled to start this summer.

Japanese firm Hitachi Zosen Corp. manufactured the machine for Seattle Tunnel Partners (STP), the contracting team that’s building the tunnel.

There’s a lot to keep track of when you’re tunneling beneath a bustling city. Steering, for instance. And of course the soil in front of the machine. The important thing to know about soil is that not all of it is the same. In fact, there are eight different types of soils along our tunnel route. In general, the looser the soil, the more likely it is to move as you tunnel through it. Sand, for example, is harder to control than clay. Other things workers might encounter underground: boulders, gravel, logs and various man-made objects.”

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